Method and mechanism for assisted diagnosis and maintenance of health monitoring system

ABSTRACT

The invention relates to a system and method of a health monitoring network which automates detection of faulty or failed sensors using real-time fault checking on a dynamically registered sensor data stream. The monitoring system and sensor network can provide a one-touch system to notify users when a sensor requires attention, without prior knowledge of the operational characteristics, installation method or configuration of sensors in the network. The network uses a decision engine to assist in maintenance according to a profile based on individual preferences and capabilities.

FIELD OF THE INVENTION

The invention relates to a system and method of a health monitoringnetwork which automates detection of faulty or failed sensors, assistsin the maintenance of, the configuration of customizable profiles basedon preferences and capabilities.

BACKGROUND

Existing solutions are designed with limited run time to avoid the needfor unsupervised system maintenance. Administration requires expertiseand training in the system. Additionally, work on multi-sensor healthmonitoring systems focuses on communication methods, data analysis, andtransducer efficacy. Practical issues in on-body multi-sensor deploymentsuch as maintaining a multi-sensor system with zero-training and minimalinconvenience is virtually non-existent.

Common methods include some form of the BIST (built-in self test) onsensor nodes, and manual inspection of data during installation andafter loss of data is detected. The execution or interpretation ofresults from these methods requires technical knowledge that most userslack. Finally, there are substantial periods of missing data when manualinspections are not regularly conducted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary embodiment in accordance with thepresent invention.

FIG. 2 illustrates an exemplary flow between the base state, messagesand sensors in accordance with an embodiment of the invention.

FIG. 3 illustrates an exemplary flow diagram of a continuous loop basedon sample rate.

FIG. 4 illustrates an exemplary flow of connection, registration anddata transfer for the sensor.

FIG. 5 illustrates an exemplary flow of data between the base stationand sensor when neither are connected.

FIG. 6 illustrates an exemplary flow of data between the base stationand sensor when the base station is connected and the sensor is notconnected.

FIG. 7 illustrates an exemplary flow of data between the base stationand sensor when both are connected and data transfer occurs.

DETAILED DESCRIPTION

The present invention relates to system design of a Health Monitoringsensor network that uses a decision engine to assist in maintenanceaccording to a profile based on individual preferences and capabilities.The invention is applicable to maintenance of physical attributes ofsensors that change over time. One embodiment is in the maintenance of asystem of battery powered sensors.

In one embodiment of the invention, there is a system and method formaintaining a network. A base station provides a user the ability toinvoke assistance in maintaining the network; at least one sensor tocommunicate status information to the base station; and a decisionengine embedded in the base station to access the status information andactivate sensor attention indicators based on a stored profile.

In one aspect of the invention, the base station bi-directionallycommunicates with the at least one sensor to determine the statusinformation and verify signal quality based upon expected range and rateof change of the sensor reading.

In another aspect of the invention, a fault-detection service checksdata of the at least one sensor, wherein the fault-detection service islocated in the base station or on a remote computing resource.

In still another aspect of the invention, the user is notified ofdetected faults on one of the at least one sensors.

In yet another aspect of the invention, the base station hosts a secure,remotely-configurable bridge to the network.

In another aspect of the invention, the at least one sensor has a visualand/or audible alarm identifiable by the user.

In still another aspect of the invention, the at least one sensor is aMEMs accelerometer.

In yet another aspect of the invention, and upon initialization ofcommunication between the base station and the at least one sensor, aregistration process occurs (see FIG. 6).

In one aspect of the invention, the registration process comprises theat least one sensor sending header information to the base stationincluding at one of the following: information about data-type forscalar quantity measure by the device, valid range, units for thescalar, frequency of delivery, and a descriptive character string; andthe base station replies with an acknowledgement message (see FIG. 6).

In another aspect of the invention, and upon receipt of an error signalfrom the base station, the at least one sensor actuates a userdetectable alarm (see FIG. 7).

In still another aspect of the invention, the decision engine iscustomizable and includes a user stored profile based on data suppliedby a healthcare provider or patient sensing requirements.

Exemplary elements of the invention are:

A) Coordinating base-station with:

-   -   1) Method for user to invoke assistance in maintaining a sensor        network.    -   2) Ability to communicate with sensors to determine status of        consumables such as power and chemical agents and verify signal        quality from affixed sensors that might “fall off” during        activity.    -   3) Physical interface to refresh depleted sensor resources.        B) Wearable sensors with:    -   1) Ability to communicate status to coordinating base-station        (as described above).    -   2) Ability to attract user attention such as a blinking        indicator or audible alarm.        C) Decision engine that can:    -   1) Access sensor status information.    -   2) Activate sensor attention indicators based on a stored        profile.    -   3) Be customized according to health care provider or patient        preferences, capabilities of the sensor and the intended        monitoring plan

In another embodiment of the invention, there is a method to provideassistance in the maintenance of a health monitoring system byautomating detection of faulty or failed sensors using real-timefault-checking on a dynamically registered sensor data stream. Themonitoring system and sensor network can provide a one-touch system tonotify users when a sensor requires attention. The user need not haveprior knowledge of the operational characteristics, installation method,or configuration of sensors in the network to unambiguously detect afault.

Additional exemplary elements are:

-   -   A base station that has the ability to conduct bi-directional        communications with sensors in the health monitoring system.        Data from each sensor is presented to a fault-detection service        for checking and the results are used to notify users of faults        on specific sensors at an opportune time. The base station hosts        a secure, remotely-configurable bridge to the local health        monitoring network.    -   A number of portable sensors that can, upon initialization,        notify the base station of the nature of their data        transmissions, and accept a message from the base station that        triggers either a visible or audible trouble indicator.    -   A fault-detection service that can select and apply        data-checking based on a library of methods associated with        specific registered data types and available computational        resources.

This invention addresses the problem(s) of:

-   -   Deploying and maintaining a long-term multi-sensor system offers        new diagnostic and intervention options for a wide range of        conditions. The adoption of these systems requires new methods        of automated assistance because in many cases the target        population has limited knowledge of technology, physical or        cognitive impairment, and limited patience for sensing systems        that further marginalize their quality of life.    -   The diminutive form-factor of on-body sensors in multi-sensor        systems requires regular intervention to maintain effectiveness        in long-term monitoring scenarios. In a multi-sensor system the        complexity of maintenance is multiplied and will require new        methods of user assistance and deployment.    -   Self-powered sensors located around users (environmental        sensors) offer advantages for mass-casualty events and other        temporary deployments. Minimizing maintenance overhead while        ensuring reliable operation is a strong product advantage.    -   The invention provides a method of assisted maintenance based on        system components that are well understood.    -   This invention simplifies the maintenance of a health monitoring        sensor system by autonomously validating data from a dynamic        group of homogeneous or heterogeneous sensors, and provides a        facile method that requires no user training for locating a        faulty sensor.    -   Examples of fault conditions include:    -   1) Sensors that are dislodged from their mounting point.    -   2) Sensors with consumable properties or limited operating        lifetime.    -   3) Sensors that become inoperable due to power transients or        corrupted memory.    -   4) Sensors that become inoperable due to tampering by visitors,        pets or pests.    -   For long term sensing, the method and mechanism described will        limit the burden on the patient according to a customizable        profile that guides a decision engine. The system will assist        the user in preventative maintenance of the sensor network at        the user's request. This method is easily adapted into the        patient's daily routine.    -   The direct result will be longer periods of multi-sensor data        capture on a wider range of individuals.    -   The consumable aspects of sensor design can be implemented with        less design margin. Relaxing design margins will result in        smaller, simpler and less expensive sensor systems providing        competitive advantage over multi-sensor systems that do not use        the techniques described.    -   The system ensures robust data collection in a dynamic sensing        environment by allowing technically naïve users to isolate        faults to a specific sensor.    -   The system relieves sensor devices with modest processing        resources of the burden of self-diagnosis.    -   The system is extensible and supports remote management and        customization.

An exemplary embodiment of one detailed application relates to the caseof a multi-limb motion capture system for physical rehabilitation, suchas stroke recovery. Referring to the embodiment in FIG. 1, ten sensorswith 7-day battery life and recording capability are placed on the body(one for each limb segment and two on the torso). Data fromaccelerometers in the sensor will be used to form a detailed model ofbody kinetics to guide treatment. The data set created by monitoring thesensors will be especially valuable since the user will be performingnatural activities. However, maintaining ten sensors, for example for2-3 weeks, is burdensome—they are easily confused and without assistancethe user will be forced to charge all ten blindly every few nights toensure battery life. The charging apparatus will be bulky andintimidating.

To assist the user and dramatically improve the usability of the sensorsystem, the proposed methods are employed using at least the followingdecision engine rules:

-   -   Ensure sensors have safety margin in remaining battery life; and    -   Indicate best sensor for charging when prompted by user for        maintenance assistance.

The patient can now maintain the sensing system, for example, based on asimple set of instructions:

-   -   1) Every night when you remove the sensors before sleep, go to        the small charging base-station and press the button.    -   2) Place the sensor with an indicator illuminated in the        base-station for maintenance (in this case data transfer and        battery charging).

Over, for example, the three week period of monitoring as describedabove, the sensors are rotated through the base-station and the simplemaintenance procedure becomes second nature much like charging acellular phone.

Referring to the embodiment in FIGS. 5+6, the base station acts asserver to sensor clients, which perform a two-step registration processduring initialization of communications. The client sends headerinformation to the base station including information includingdata-type for scalar quantity measured by the device, valid range, unitsfor the scalar, frequency of delivery, and a descriptive characterstring. The base station replies with an acknowledgement message.

The base station calls a fault detection service to check sensor datafor proper operation. A simple example would be to perform temporal andscalar bounds-checking for each sensor's data stream with aberrantvalues measured against the device's recent historical trend. A morecomplex system may use modeling and machine learning techniques toqualify the sensed data using additional data sources (time of day,season, etc.)

Sensors can be quite different or have subtle failure modes makingmanual checking tedious for humans, but the process is easily automatedusing the method herein described.

The fault detection service can be hosted in the base station or on aremote computing resource depending on the processing requirements.

The sensor acts as client to base station server, but listens forspurious messages from server. After registration, sensor minimizescommunications to data transmission. Upon receipt of an error signalfrom base station, the sensor actuates a human-detectable alarm, forexample, a low power blinking LED. A one-touch-for-maintenance systemmay log a sensor fault but wait for a user button-press to signal afault.

Referring to the tables below, one method of sensor operating lifecalculation is to use average current during a repeated sampling windowaccording to the following equation:

IAvg=(tStore×IStore)+(tComm×IComm)+[(tWindow−Store−tComm)×IAcq)]  (1)

MEMs accelerometers are useful sensors. The following table waspopulated based on the operating specifications of an ultra-low powerCPU acquiring 16 bit samples for X-Y-Z data using DMA and power savingmodes (subject to timing constraints).

Sampling Rate (Hz), use IAcq (mA) Bits per second 10, activitysegmentation .090 480 50, gesture recognition .44 2400 100, clinicalgrade .90 4800 measurement

Using conservative values of 20 mA for IStore (better thenstate-of-the-art for reliable standards based wireless communication orflash media) and an aggressive transfer rate of 0.5 Mbps the followingtable can be computed using the previous table and equation 1. The tableshows best case sensor operating life for 4 common form factors:

Key- Button, Fob, Sampling IAvg 100 250 Pager, Phone, Rate (Hz)tStore(s) (mA) mAh mAh 500 mAh 1000 mAh 10 .001 .12 35 days 87 days 174days  350 days 50 .005 .30 14 days 35 days 69 days 140 days 100 .01 .59 7 days 18 days 35 days  70 days

Adding extra degrees of sensing will result in even shorter operatinglife—e.g. ½ as long when collecting all 6-axis of motion.

Returning to the case of a clinical grade gait and motion capture systemusing 9 sensors, each sensor would require a 500 mAh battery for onemonth of data capture. The proposed system for assisted maintenancewould allow the user to continuously rotate through considerably smallersensors without guidance from a caregiver. For example, a key-fob sizeddevice would provide margin and a single sensor could be recharged everynight. If the sensor system requires wireless communication, real-worlddata transfer rates can be up to 100× worse then the numbers above dueto packet loss

Alternatively, in a preferred embodiment with reference to Table 10 andFIG. 7, sensor operation is repetitive and can be expressed as arepetitive loop consisting of states for data acquisition, data storage,data communication, and sensor idle. Over time, the average powerconsumed by the sensor will be equal to a sum of terms for power in eachstate weighted by time spent in each state. In the likely worst case,current draw for each state can be determined from a static value fromdevice datasheets.

For battery powered devices, power is approximated by =Current draw on abattery with a manufacturer's mAh rating. Therefore power in a state isapproximated by current, not current*voltage.

From these assertions, an equation for average current in a repetitiveloop is derived:

Average Current/Many Identical Loops˜=Current/Loop

Average Current=[Time spent storing*Current while storing]+[Time spentcommunicating*Current while communicating]+[Time spent in setup toacquiring data*Current in setup to acquiring data)+[Time spent acquiringdata*Current while acquiring data]+[Time spent Idle*Currrent while Idle]

IAvg=[tStore*IStore]+[tComm*IComm]+[tSetup*ISetup]+[tAcq*IAcq]+[tIdle*IIdle]  (1)

It can be observed that:

tLoop=tStore+tComm+tSetup+tAcq+tIdle  (2)

To simplify notation, an average current for Setup, Acquire and Idlestates is calculated as illustrated in 100 Hz Sampling table 10:

The acquisition process uses data from datasheets for timingrequirements and current consumption (eg. 1.3mA=ICPUinDMA+IADC+IAccelerometer) and involves the following states:

1) Idle;

2) Enable on the accelerometer so that power can stabilize (setup toAcquiring data); and

3) Enable the ADC and sample X/Y/Z data points.

The number in the time row is the sample period, the number below is thecalculated average current.

Bits per second can be calculated easily:

Samples per second*bits per sample*channels sampled=bits per second.

-   -   For 10 Hz:

10*16*3=480 bps

For 50 Hz, the value is 2400 bps

For 100 Hz the value is 4800 bps

From this we get the completed first and second tables above.

So:

IAvg=[tStore*IStore]+[0*IComm]+[tSampling*ISampling]  (2)

See Continuous Loop based on Sample Rate (FIG. 7).tStore=Bits per second/data transfer rate.tSampling and ISample are calculated based on the sample rate chartabove.

The second table above is based on plugging results to equation (1)using Istore=20 ma and a data transfer rate of 0.5 Mbps. Also tComm isset to zero since Istore is less then IComm in most cases.

For 10 Hz and communication every second:

Iavg=((0.001 s)*20 mA)+(1 s−0.001 s)*0.091 mA=0.11 mA

For 50 Hz and communication every second:

Iavg=((0.005 s)*20 mA)+(1 s−0.005 s)*0.44 mA=0.53 mA

For 100 Hz and communication every second:

Iavg=((0.01 s)*20 mA)+(1 s−0.010 s)*0.88 mA=1.1 mA

Finally, battery life is calculated using the formula:

Operating life(hrs)=[(Battery capacity(mAh)/Iavg)]

Operating life days=Operating life hrs/24

For 10 Hz:

100 mAh/0.11 ma=909 hrs=38 days

250 mAh/0.11 ma=2272 hrs=95 days

500 mAh/0.11 ma=4545 hrs=189 days

1000 mAh/0.11 ma=9091 hrs=379 days

For 50 Hz:

100 mAh=8 days

250 mAh=20 days

500 mAh=39. days

1000 mAh=79 days

For 100 Hz:

100 mAh=4 days

250 mAh=10 days

500 mAh=19 days

1000 mAh=38 days

Most sensors are electrical or electronic, although other types exist. Asensor is a type of transducer. Direct indicating sensors, for example,a mercury thermometer, are human readable. Other sensors must be pairedwith an indicator or display, for instance a thermocouple.

Sensors are used in everyday life. Applications include automobiles,machines, aerospace, medicine, industry and robotics.

Technical progress allows more and more sensors to be manufactured withMEMS technology. In most cases this offers the potential to reach a muchhigher sensitivity. See also MEMS sensor generations.

Types

Since a significant change involves an exchange of energy, sensors canbe classified according to the type of energy transfer that they detect.

Thermal

-   -   Temperature sensors: thermometers, thermocouples, temperature        sensitive resistors (thermistors and resistance temperature        detectors), bi-metal thermometers and thermostats.    -   Heat sensors: bolometer, calorimeter.

Electromagnetic

-   -   Electrical resistance sensors: ohmmeter, multimeter    -   Electrical current sensors: galvanometer, ammeter    -   Electrical voltage sensors: leaf electroscope, voltmeter    -   Electrical power sensors: watt-hour meters    -   Magnetism sensors: magnetic compass, fluxgate compass,        magnetometer, Hall effect device,    -   Metal detectors

Mechanical

-   -   Pressure sensors: altimeter, barometer, barograph, pressure        gauge, air speed indicator, rate of climb indicator, variometer    -   Gas and liquid flow sensors: flow sensor, anemometer, flow        meter, gas meter, water meter, mass flow sensor    -   Mechanical sensors: acceleration sensor, position sensor,        selsyn, switch, strain gauge

Chemical

Chemical sensors detect the presence of specific chemicals or classes ofchemicals. Examples include oxygen sensors, also known as lambdasensors, ion-selective electrodes, pH glass electrodes, and redoxelectrodes.

Optical and Radiation

Electromagnetic time-of-flight. Generate an electromagnetic impulse,broadcast it, then measure the time a reflected pulse takes to return.Commonly known as—RADAR (Radio Detection And Ranging) are nowaccompanied by the analogous LIDAR (Light Detection And Ranging. Seefollowing line), all being electromagnetic waves. Acoustic sensors are aspecial case in that a pressure transducer is used to generate acompression wave in a fluid medium (air or water) light time-of-flight.Used in modern surveying equipment, a short pulse of light is emittedand returned by a retroreflector. The return time of the pulse isproportional to the distance and is related to atmospheric density in apredictable way.

Ionising Radiation

Radiation sensors: Geiger counter, dosimeter, Scintillation counter,Neutron detection.

Subatomic sensors: Particle detector, scintillator, Wire chamber, cloudchamber, bubble chamber. See Category:Particle_detectors

Non-Ionising Radiation

-   -   Light sensors, or photodetectors, including semiconductor        devices such as photocells, photodiodes, phototransistors, CCDs,        and Image sensors; vacuum tube devices like photo-electric        tubes, photomultiplier tubes; and mechanical instruments such as        the Nichols radiometer.    -   Infrared sensor, especially used as occupancy sensor for        lighting and environmental controls.    -   Proximity sensor—A type of distance sensor but less        sophisticated. Only detects a specific proximity. May be        optical—combination of a photocell and LED or laser.        Applications in cell phones, paper detector in photocopiers,        auto power standby/shutdown mode in notebooks and other devices.        May employ a magnet and a Hall effect device.    -   Scanning laser—A narrow beam of laser light is scanned over the        scene by a mirror. A photocell sensor located at an offset        responds when the beam is reflected from an object to the        sensor, whence the distance is calculated by triangulation.    -   Focus. A large aperture lens may be focused by a servo system.        The distance to an in-focus scene element may be determined by        the lens setting.    -   Binocular. Two images gathered on a known baseline are brought        into coincidence by a system of mirrors and prisms. The        adjustment is used to determine distance. Used in some cameras        (called range-finder cameras) and on a larger scale in early        battleship range-finder    -   Interferometry. Interferencefringes between transmitted and        reflected lightwaves produced by a coherent source such as a        laser are counted and the distance is calculated. Capable of        extremely high precision.    -   Scintillometers measure atmospheric optical disturbances.

Acoustic

-   -   Sound sensors: microphones, hydrophones, seismometers.    -   Acoustic: uses ultrasound time-of-flight echo return. Used in        mid 20th century polaroid cameras and applied also to robotics.        Even older systems like Fathometers (and fish finders) and other        ‘Tactical Active’ Sonar (Sound Navigation And Ranging) systems        in naval applications which mostly use audible sound        frequencies.

Other Types

-   -   Motion sensors: radar gun, speedometer, tachometer, odometer,        occupancy sensor, turn coordinator    -   Orientation sensors: gyroscope, artificial horizon, ring laser        gyroscope    -   Distance sensor (noncontacting) Several technologies can be        applied to sense distance: magnetostriction

Non Initialized Systems

Gray code strip or wheel—a number of photodetectors can sense a pattern,creating a binary number. The gray code is a mutated pattern thatensures that only one bit of information changes with each measuredstep, thus avoiding ambiguities.

Initialized Systems

These require starting from a known distance and accumulate incrementalchanges in measurements.

-   -   Quadrature wheel—An disk-shaped optical mask is driven by a gear        train. Two photocells detecting light passing through the mask        can determine a partial revolution of the mask and the direction        of that rotation.    -   Whisker sensor—A type of touch sensor and proximity sensor.

Microelectromechanical Systems (MEMS): is the technology of the verysmall, and merges at the nanoscale into “Nanoelectromechanical” Systems(NEMS) and Nanotechnology. In Europe, MEMS are often referred to asMicro Systems Technology (MST). It should not be confused with thehypothetical vision of Molecular nanotechnology or MolecularElectronics. These devices generally range in size from a micrometer (amillionth of a meter) to a millimeter (thousandth of a meter). At thesesize scales, a human's intuitive sense of physics does not always holdtrue. Due to MEMS' large surface area to volume ratio, surface effectssuch as electrostatics and wetting dominate volume effects such asinertia or thermal mass. They are fabricated using modified siliconfabrication technology (used to make electronics), molding and plating,wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electrodischarge machining (EDM), and other technologies capable ofmanufacturing very small devices. MEMS sometimes go by the namesmicromechanics, micro machines, or micro system technology (MST).

Companies with strong MEMS programs come in many sizes. The larger firmsspecialize in manufacturing high volume inexpensive components orpackaged solutions for end markets such as automobiles, biomedical, andelectronics. The successful small firms provide value in innovativesolutions and absorb the expense of custom fabrication with high salesmargins. In addition, both large and small companies work in R&D toexplore MEMS technology. Complexity and performance of advanced MEMSbased sensors are described by different MEMS sensor generations.

Common applications include:

-   -   Inkjet printers, which use piezoelectrics or bubble ejection to        deposit ink on paper.    -   Accelerometers in modern cars for a large number of purposes        including airbag deployment in collisions.    -   MEMS gyroscopes used in modern cars and other applications to        detect yaw; e.g. to deploy a roll over bar or trigger dynamic        stability control.    -   Pressure sensors e.g. car tire pressure sensors, and disposable        blood pressure sensors.    -   Displays e.g the DMD chip in a projector based on DLP technology        has on its surface several hundred thousand micromirrors.    -   Optical switching technology which is used for switching        technology for data communications, and is part of the emerging        technology of smartdust.    -   The motion-sensing controller in the Nintendo Wii video game        system represents a popular consumer application of MEMS        technology.    -   Finite element analysis is an important part of MEMS design.

Flash memory: is a form of non-volatile computer memory that can beelectrically erased and reprogrammed. It is a technology that isprimarily used in memory cards. Unlike EEPROM, it is erased andprogrammed in blocks consisting of multiple locations (in early flashthe entire chip had to be erased at once). Flash memory costs far lessthan EEPROM and therefore has become the dominant technology wherever asignificant amount of non-volatile, solid-state storage is needed.Examples of applications include digital audio players, digital camerasand mobile phones. Flash memory is also used in USB flash drives (thumbdrives, handy drive), which are used for general storage and transfer ofdata between computers. It has also gained some popularity in the gamingmarket, where it is often used instead of EEPROMs or battery-poweredSRAM for game save data.

Automation: roboticization or industrial automation or numerical controlis the use of control systems such as computers to control industrialmachinery and processes, replacing human operators. In the scope ofindustrialization, it is a step beyond mechanization. Whereasmechanization provided human operators with machinery to assist themwith the physical requirements of work, automation greatly reduces theneed for human sensory and mental requirements as well.

There are still many jobs which are in no immediate danger ofautomation. No device has been invented which can match the human eyefor accuracy and precision in many tasks; nor the human ear. Even theadmittedly handicapped human is able to identify and distinguish amongfar more scents than any automated device. Human pattern recognition,language recognition, and language production ability is well beyondanything currently envisioned by automation engineers.

Specialized hardened computers, referred to as programmable logiccontrollers (PLCs), are frequently used to synchronize the flow ofinputs from (physical) sensors and events with the flow of outputs toactuators and events. This leads to precisely controlled actions thatpermit a tight control of almost any industrial process. (It was thesedevices that were feared to be vulnerable to the “Y2K bug”, with suchpotentially dire consequences, since they are now so ubiquitousthroughout the industrial world.)

The process of circuit design can cover systems ranging from nationalpower grids all the way down to the individual transistors within anintegrated circuit. For simple circuits the design process can often bedone by one person without needing a planed or structured designprocess, but for more complex designs, teams of designers following asystematic approach with intelligently guided computer simulation arebecoming increasingly common.

Formal circuit design usually involves the following stages:

-   -   Sometimes, writing the requirement specification after liaising        with the customer    -   Writing a technical proposal to meet the requirements of the        customer specification    -   Synthesising on paper an abstract electrical or electronic        circuit that will meet the specifications    -   Calculating the component values to meet the operating        specifications under specified conditions    -   Building a breadboard or other prototype version of the design        and testing against specification    -   Making any alterations to the circuit to achieve compliance    -   Choosing a method of construction as well as all the parts and        materials to be used    -   Presenting component and layout information to draughtspersons,        and layout and mechanical engineers, for prototype production    -   Testing or type-testing a number of prototypes to ensure        compliance with customer requirements    -   Signing and approving the final manufacturing drawings    -   Post-design services (obsolescence of components etc.)

Specification

The process of circuit design begins with the specification, whichstates the functionality that the finished design must provide, but doesnot indicate how it is to be achieved. The initial specification isbasically a technically detailed description of what the customer wantsthe finished circuit to achieve and can include a variety of electricalrequirements, such as what signals the circuit will receive, whatsignals it must output, what power supplies are available and how muchpower it is permitted to consume. The specification can (and normallydoes) also set some of the physical parameters that the design mustmeet, such as size, weight, moisture resistance, temperature range,thermal output, vibration tolerance and acceleration tolerance.

As the design process progresses the designer(s) will frequently returnto the specification and alter it to take account of the progress of thedesign. This can involve tightening specifications that the customer hassupplied, and adding tests that the circuit must pass in order to beaccepted. These additional specifications will often be used in theverification of a design. Changes that conflict with or modify thecustomer's original specifications will almost always have to beapproved by the customer before they can be acted upon.

Correctly identifying the customer needs can avoid a condition known as‘design creep’ which occurs in the absence of realistic initialexpectations, and later by failing to communicate fully with the clientduring the design process. It can be defined in terms of its results;“at one extreme is a circuit with more functionality than necessary, andat the other is a circuit having an incorrect functionality”. (DeMers,1997) Nevertheless some changes can be expected and it is good practiceto keep options open for as long as possible because it's easier toremove spare elements from the circuit later on than it is to put themin.

Design

The design process involves moving from the specification at the start,to a plan that contains all the information needed to be physicallyconstructed at the end, this normally happens by passing through anumber of stages, although in very simple circuit it may be done in asingle step. The process normally begins with the conversion of thespecification into a block diagram of the various functions that thecircuit must perform, at this stage the contents of each block are notconsidered, only what each block must do, this is sometimes referred toas a “black box” design. This approach allows the possibly verycomplicated task to be broken into smaller tasks which may either bytackled in sequence or divided amongst members of a design team.

Each block is then considered in more detail, still at an abstractstage, but with a lot more focus on the details of the electricalfunctions to be provided. At this or later stages it is common torequire a large amount of research or mathematical modeling into what isand is not feasible to achieve. The results of this research may be fedback into earlier stages of the design process, for example if it turnsout one of the blocks cannot be designed within the parameters set forit, it may be necessary to alter other blocks instead. At this point itis also common to start considering both how to demonstrate that thedesign does meet the specifications, and how it is to be tested (whichcan include self diagnostic tools).

Finally the individual circuit components are chosen to carry out eachfunction in the overall design, at this stage the physical layout andelectrical connections of each component are also decided, this layoutcommonly taking the form of artwork for the production of a printedcircuit board or Integrated circuit. This stage is typically extremelytime consuming because of the vast array of choices available. Apractical constraint on the design at this stage is that ofstandardization, while a certain value of component may be calculatedfor use in some location in a circuit, if that value cannot be purchasedfrom a supplier, then the problem has still not been solved. To avoidthis a certain amount of ‘catalog engineering’ can be applied to solvethe more mundane tasks within an overall design.

Costs

Proper design philosophy incorporates economic and technicalconsiderations and keeps them in balance at all times, and right fromthe start. Balance is the key concept here; just as many delays andpitfalls can come from ill considered cost cutting as with costoverruns. Good accounting tools (and a design culture that fosters theiruse) is imperative for a successful project. “Manufacturing costs shrinkas design costs soar,” is oft quoted as a truism in circuit design,particularly for IC's.

Verification and Testing

Once a circuit has been designed, it must be both verified and tested.Verification is the process of going through each stage of a design andensuring that it will do what the specification requires it to do. Thisis frequently a highly mathematical process and can involve large-scalecomputer simulations of the design. In any complicated design it is verylikely that problems will be found at this stage and may involve a largeamount of the design work be redone in order to fix them

Testing is the real-world counterpart to verification, testing involvesphysically building at least a prototype of the design and then (incombination with the test procedures in the specification or added toit) checking the circuit really does do what it was designed to.

Prototyping

Prototyping is a means of exploring ideas before an investment is madein them. Depending on the scope of the prototype and the level of detailrequired, prototypes can be built at any time during the project.Sometimes they are created early in the project, during the planning andspecification phase, commonly using a process known as breadboarding;that's when the need for exploration is greatest, and when the timeinvestment needed is most viable. Later in the cycle packaging mock-upsare used to explore appearance and usability, and occasionally a circuitwill need to be modified to take these factors into account.

Results

As circuit design is the process of working out the physical form thatan electronic circuit will take, the result of the circuit designprocess is the instructions on how to construct the physical electroniccircuit. This will normally take the form of blueprints describing thesize, shape, connectors, etc in use, and artwork or CAM file formanufacturing a printed circuit board or Integrated circuit.

Documentation

Any commercial design will normally also include an element ofdocumentation, the precise nature of this documentation will varyaccording to the size and complexity of the circuit as well as thecountry in which it is to be used. As a bare minimum the documentationwill normally include at least the specification and testing proceduresfor the design and a statement of compliance with current regulations.In the EU this last item will normally take the form of a CE Declarationlisting the European directives complied with and naming an individualresponsible for compliance.

1. A system for maintaining a sensor network, comprising: sensor networkcomprising at least one sensor; a base station adapted to receive datafrom the sensor network; the at least one sensor being adapted tocommunicate data to the base station; a fault-detection system adaptedto analyze data from the at least one sensor and determine an operatingstate of the at least one sensor, wherein the fault-detection system islocated in the base station or on a remote computing resource; and adecision engine embedded in the base station or on the remote computingsource, the decision engine being adapted to activate a sensor attentionindicator based on an output from the fault-detection system indicativeof an operating state of the at least one sensor.
 2. The system of claim1, wherein the base station bi-directionally communicates with the atleast one sensor
 3. (canceled)
 4. The system of claim 1, wherein thesystem is adapted to notify a detected fault on the at least one sensor.5. The system of claim 1, wherein the base station hosts a secure,remotely-configurable bridge to the sensor network.
 6. The system ofclaim 4, wherein the at least one sensor comprises a visual and/oraudible alarm.
 7. The system of claim 1, wherein the at least one sensoris a MEMs accelerometer.
 8. The system of claim 1, wherein uponinitialization of communication between the base station and the atleast one sensor, the system is adapted to start a registration process.9. The system of claim 1, wherein: the at least one sensor is adapted tosend header information to the base station including at least one ofthe following: information about data-type for scalar quantity measureby the device, valid range, units for the scalar, frequency of delivery,and a descriptive character string; and the base station is adapted toreply with an acknowledgement message.
 10. The system of claim 1,wherein upon receipt of an error signal from the base station, the atleast one sensor actuates a detectable alarm.
 11. The system of claim 1,wherein the decision engine includes a user stored profile based on datasupplied by a healthcare provider or a patient.
 12. A method formaintaining a sensor network, comprising: providing the sensor networkcomprising at least one sensor; providing a base station adapted toreceive data from the sensor network; the at least one sensor beingadapted to communicate data to the base station; providing afault-detection system adapted to analyze data from the at least onesensor and determine an operating state of the at least one sensor,wherein the fault-detection system is located in the base station or ona remote computing resource; and providing a decision engine embedded inthe base station or on the remote computing source, the decision enginebeing adapted to activate a sensor attention indicator based on anoutput from the fault-detection system indicative of an operating stateof the at least one sensor.
 13. The method of claim 12, wherein the basestation bi-directionally communicates with the at least one sensor 14.(canceled)
 15. The method of claim 12, wherein the system is adapted tonotify a detected fault on the at least one sensor.
 16. The method ofclaim 12, wherein the base station hosts a secure, remotely-configurablebridge to the sensor network.
 17. The method of claim 15, wherein the atleast one sensor comprises a visual and/or audible alarm.
 18. The methodof claim 12, wherein the at least one sensor is a MEMs accelerometer.19. The method of claim 12, wherein upon initialization of communicationbetween the base station and the at least one sensor, the system isadapted to start a registration process.
 20. The method of claim 19,wherein the registration process comprises: sending, via the at leastone sensor, header information to the base station including at leastone of the following: information about data-type for scalar quantitymeasure by the device, valid range, units for the scalar, frequency ofdelivery, and a descriptive character string; and replying, via the basestation, with an acknowledgement message.
 21. The method of claim 12,wherein upon receipt of an error signal from the base station, the atleast one sensor actuates a detectable alarm.
 22. The method of claim12, wherein the decision engine includes a user stored profile based ondata supplied by a healthcare provider or a patient.